This invention is concerned with a method of marking forms such as confectionery products, food, pharmaceutical tablets, and hard and soft gelatin capsules with a water based ingestible ink.
Reference is made to James C. Brown U.S. Pat. No. 3,258,347 issued on Jun. 28, 1966 for "Edible Pharmaceutical Ink"; Roy Y. Sanders, Jr. U.S. Pat. No. 2,948,626 issued on Aug. 9, 1960 for "Edible Pharmaceutical Ink and Process of Using Same"; Chester J. Piotrowski U.S. Pat. No. 3,694,237 issued on Sep. 26, 1972 for "Edible Ink"; and Stuart C. Porter et al. U.S. Pat. No. 4,543,370 issued on Sep. 24, 1985 for "Dry Edible Film Coating Composition, Method and Coating Form". These patents are incorporated herein by reference.
Prior art ingestible inks suitable for marking forms such as confectionery products, food, pharmaceutical tablets, and hard and soft gelatin capsules have a shellac base in ethyl alcohol. One of the problems in marking such forms and one of the more important parameters for these inks is drying time. Brown U.S. Pat. No. 3,258,347, which refers to drying time as "set-to-touch-time", states that the optimum transfer characteristics of the ink are obtained when the set-to-touch-time is two to four minutes. When the drying time is too slow, as is discussed in Sanders, Jr. U.S. Pat. No. 2,948,626, a tackiness problem develops resulting in spotting or smudging of the ink. Drying time is also discussed in Piotrowski U.S. Pat. No. 3,694,237 at column 1, lines 57-72 which states: "Prior art edible inks are made with dry shellac, ethyl alcohol, plasticizers and/or detackifiers, pigments, or dyes, and solvents which give a desired drying time, say three minutes. As the ink ages, a process occurs wherein the acid groups of the shellac react with the ethyl alcohol to form an ethyl ester of the shellac. The presence of the shellac ester increases the drying time of the ink, and as the amount or percentage of ester increases, the drying time is increased, eventually to a point where the drying time is too long, causing offset, or pick-off, or transfer of the ink from one printed piece or tablet to another. Accordingly, it has been noted that the drying time of prior art inks increases with age, and this limits the shelf or storage life of the ink."
The machines presently being used to print marks onto pharmaceutical, food or confectionery products use a principle that is best described as offset gravure. An engraved cylinder picks up ink as it rotates in an ink bath. Excess ink is wiped off the engraved cylinder by a doctor blade and the ink remaining in the gravure etch of the cylinder is transferred to a rubber transfer (offset) roller which rotates with its roller surface in contact with the engraved cylinder. The ink on the transfer roller is then deposited onto the end product such as a tablet, or capsule.
The form may have been film coated, sugar coated, or not coated at all. To date, almost all inks used for this purpose have been of a shellac base in ethyl alcohol. While some shellac based inks have incorporated some water into the formula by the modification of pH, the inks remain alcohol based for the most part. Accordingly, their closed cup flash point is less than 100.degree. F., and, therefore, they must be labeled as a hazardous flammable liquid.